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Cancer cells adeptly manipulate their metabolic processes to evade immune detection, a phenomenon intensifying the complexity of cancer progression and therapy. This review delves into the critical role of cancer cell metabolism in the immune-editing landscape, highlighting how metabolic reprogramming facilitates tumor cells to thrive despite immune surveillance pressures. We explore the dynamic interactions within the tumor microenvironment (TME), where cancer cells not only accelerate their glucose and amino acid metabolism but also induce an immunosuppressive state that hampers effective immune response. Recent findings underscore the metabolic competition between tumor and immune cells, particularly focusing on how this interaction influences the efficacy of emerging immunotherapies. By integrating cutting-edge research on the metabolic pathways of cancer cells, such as the Warburg effect and glutamine addiction, we shed light on potential therapeutic targets. The review proposes that disrupting these metabolic pathways could enhance the response to immunotherapy, offering a dual-pronged strategy to combat tumor growth and immune evasion.

Natural killer (NK) cells are innate lymphocytes that rapidly respond to cancer cells without prior sensitization or restriction to the cognate antigen in comparison with tumor antigen‐specific T cells. Recent advances in understanding NK‐cell biology have elucidated the molecular mechanisms underlying the differentiation and maturation of NK cells, in addition to the control of their effector functions by investigating the receptors and ligands involved in the recognition of cancer cells by NK cells. Such clarification of NK‐cell recognition of cancer cells also revealed the mechanism by which cancer cells potentially evade NK–cell‐dependent immune surveillance. Furthermore, the recent clinical results of T–cell‐targeted cancer immunotherapy have increased the expectations for new immunotherapies by targeting NK cells. However, the potential use of NK cells in cancer immunotherapy is not fully understood. In this review, we discuss the current evidence and future potential of pharmacological targeting of NK cells in cancer immunotherapy. There are several pharmacological targets that can be used to develop cancer immunotherapies that function by controlling NK cells via their activation or strengthening their cancer cell recognition. The use of NK cells in adoptive cancer immunotherapy is also expected.

BackgroundResistance to an immune checkpoint inhibitor (ICI) is a major obstacle in cancer immunotherapy. The causes of ICI resistance include major histocompatibility complex (MHC)/histocompatibility locus antigen (HLA) class I loss, neoantigen loss, and incomplete antigen presentation. Elimination by natural killer (NK) cells would be expected to be an effective strategy for the treatment of these ICI-resistant tumors. We previously demonstrated that a lipid nanoparticle containing a stimulator of an interferon gene (STING) agonist (STING-LNP) efficiently induced antitumor activity via the activation of NK cells. Thus, we evaluated the potential of reducing ICI resistance by STING-LNPs.MethodsLung metastasis of a B16-F10 mouse melanoma was used as an anti-programmed cell death 1 (anti-PD-1)-resistant mouse model. The mice were intravenously injected with the STING-LNP and the mechanism responsible for the improvement of anti-PD-1 resistance by the STING-LNPs was analyzed by RT-qPCR and flow cytometry. The dynamics of STING-LNP were also investigated.ResultsAlthough anti-PD-1 monotherapy failed to induce an antitumor effect, the combination of the STING-LNP and anti-PD-1 exerted a synergistic antitumor effect. Our results indicate that the STING-LNP treatment significantly increased the expression of CD3, CD4, NK1.1, PD-1 and interferon (IFN)-γ in lung metastases. This change appears to be initiated by the type I IFN produced by liver macrophages that contain the internalized STING-LNPs, leading to the systemic activation of NK cells that express PD-1. The activated NK cells appeared to produce IFN-γ, resulting in an increase in the expression of the PD ligand 1 (PD-L1) in cancer cells, thus leading to a synergistic antitumor effect when anti-PD-1 is administered.ConclusionsWe provide a demonstration to show that a STING-LNP treatment can overcome PD-1 resistance in a B16-F10 lung metastasis model. The mechanism responsible for this indicates that NK cells are activated by stimulating the STING pathway which, in turn, induced the expression of PD-L1 on cancer cells. Based on the findings reported herein, the STING-LNP represents a promising candidate for use in combination therapy with anti-PD-1-resistant tumors.

Thalidomide and its analogues are known as immunomodulatory drugs (IMiDs) that possess direct antimyeloma effects, in addition to other secondary effects, including antiangiogenic, antiinflammatory, and immunomodulatory effects. Although the involvement of natural killer (NK) cells in the antitumor effects of IMiDs has been reported, it is unclear whether IMiDs inhibit cancer cell metastasis by regulating the antitumor function of NK cells. In this study, we examined the protective effects of thalidomide against cancer metastasis by focusing on its immunomodulatory effects through NK cells. Using experimental lung metastasis models, we found that pharmacological effects of thalidomide on host cells, but not its direct anticancer tumor effects, are responsible for the inhibition of lung metastases. To exert the antimetastatic effects of thalidomide, both γ‐interferon (IFN‐γ) production and direct cytotoxicity of NK cells were essential, without notable contribution from T cells. In thalidomide‐treated mice, there was a significant increase in the terminally differentiated mature CD27lo NK cells in the peripheral tissues and NK cells in thalidomide‐treated mice showed significantly higher cytotoxicity and IFN‐γ production. The NK cell expression of T‐bet was upregulated by thalidomide treatment and the downregulation of glycogen synthase kinase‐3β expression was observed in thalidomide‐treated NK cells. Collectively, our study suggests that thalidomide induces the functional maturation of peripheral NK cells through alteration of T‐bet expression to inhibit lung metastasis of cancer cells. In this study, we examined the antimetastatic effects of thalidomide by focusing on its immunomodulatory effects through natural killer (NK) cells. Our study suggests that thalidomide induces the functional maturation of peripheral NK cells likely through alteration of T‐bet expression, to inhibit lung metastasis of cancer cells.

Bacterial metabolites recognized by STING Cyclic dinucleotides, used as signalling molecules in bacteria but not in mammalian cells, are recognized by the mammalian innate immune system, triggering the production of type I interferon. Here the mammalian protein STING (stimulator of IFN genes) is identified as the direct molecular sensor for cyclic diguanylate monophosphate and other cyclic dinucleotides. Previously, STING was thought to act solely as a downstream signalling adaptor. Cyclic dinucleotides are potent immunostimulants, and may prove useful therapeutically. The innate immune system detects infection by using germline-encoded receptors that are specific for conserved microbial molecules. The recognition of microbial ligands leads to the production of cytokines, such as type I interferons (IFNs), that are essential for successful pathogen elimination. Cytosolic detection of pathogen-derived DNA is one major mechanism of inducing IFN production 1 , 2 , and this process requires signalling through TANK binding kinase 1 (TBK1) and its downstream transcription factor, IFN-regulatory factor 3 (IRF3). In addition, a transmembrane protein called STING (stimulator of IFN genes; also known as MITA, ERIS, MPYS and TMEM173) functions as an essential signalling adaptor, linking the cytosolic detection of DNA to the TBK1–IRF3 signalling axis 3 , 4 , 5 , 6 , 7 . Recently, unique nucleic acids called cyclic dinucleotides, which function as conserved signalling molecules in bacteria 8 , have also been shown to induce a STING-dependent type I IFN response 9 , 10 , 11 , 12 . However, a mammalian sensor of cyclic dinucleotides has not been identified. Here we report evidence that STING itself is an innate immune sensor of cyclic dinucleotides. We demonstrate that STING binds directly to radiolabelled cyclic diguanylate monophosphate (c-di-GMP), and we show that unlabelled cyclic dinucleotides, but not other nucleotides or nucleic acids, compete with c-di-GMP for binding to STING. Furthermore, we identify mutations in STING that selectively affect the response to cyclic dinucleotides without affecting the response to DNA. Thus, STING seems to function as a direct sensor of cyclic dinucleotides, in addition to its established role as a signalling adaptor in the IFN response to cytosolic DNA. Cyclic dinucleotides have shown promise as novel vaccine adjuvants and immunotherapeutics 9 , 13 , and our results provide insight into the mechanism by which cyclic dinucleotides are sensed by the innate immune system.

Accumulating evidence indicates the importance of natural killer (NK) cells in controlling tumor growth and metastasis. NK cell subsets display diversities in their function and tissue distribution and Mac‐1hi CD27lo NK cells are the predominant population of lung‐resident NK cells. Although the lung is a major organ where primary tumor develops and cancer cells metastasize, there is no clear evidence whether circulating NK cells and/or tissue‐resident NK cells control tumor growth in the lung. In the present study, we examined an antitumor function of lung‐resident NK cells to control pulmonary tumor growth. In an orthotopic lung tumor model, NK cells controlled pulmonary tumor growth, and mature circulating NK cell subsets were increased in tumor‐bearing lungs through a C‐X‐C motif chemokine receptor 3 (CXCR3)‐dependent mechanism. Although such increase in migratory NK cell subsets can be blocked by anti‐CXCR3 treatment, there was no difference in pulmonary tumor growth in anti‐CXCR3‐treated mice compared with control mice. In addition to pulmonary tumor growth, lung‐resident NK cells, but not migratory NK cells, play a dominant role in controlling metastatic growth of cancer cells in lung. These results strongly indicate an importance of lung‐resident NK cells for controlling pulmonary tumor growth. Although lung is a major organ where primary tumor develops and cancer cells metastasize, there is no clear evidence whether circulating NK cells and/or tissue‐resident NK cells control tumor growth in lung. Presented results indicate the importance of lung‐resident NK cells for controlling pulmonary tumor growth.

Cancer metastasis is a major cause of the high mortality rate in lung cancer patients. The cytoskeletal rearrangement and degradation of extracellular matrix are required to facilitate cell migration and invasion and the suppression of these behaviors is an intriguing approach to minimize cancer metastasis. Even though Erianthridin (ETD), a phenolic compound isolated from the Thai orchid Dendrobium formosum exhibits various biological activities, the molecular mechanism of ETD for anti-cancer activity is unclear. In this study, we found that noncytotoxic concentrations of ETD (≤ 50 μM) were able to significantly inhibit cell migration and invasion via disruption of actin stress fibers and lamellipodia formation. The expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 was markedly downregulated in a dose-dependent manner after ETD treatment. Mechanistic studies revealed that protein kinase B (Akt) and its downstream effectors mammalian target of rapamycin (mTOR) and p70 S6 kinase (p70 S6K ) were strongly attenuated. An in silico study further demonstrated that ETD binds to the protein kinase domain of Akt with both hydrogen bonding and van der Waals interactions. In addition, an in vivo tail vein injection metastasis study demonstrated a significant effect of ETD on the suppression of lung cancer cell metastasis. This study provides preclinical information regarding ETD, which exhibits promising antimetastatic activity against non-small-cell lung cancer through Akt/mTOR/p70 S6K -induced actin reorganization and MMPs expression.

Genetic evolution that occurs during cancer progression enables tumour heterogeneity, thereby fostering tumour adaptation, therapeutic resistance and metastatic potential. Immune responses are known to select (immunoedit) tumour cells displaying immunoevasive properties. Here we address the role of IFN-γ in mediating the immunoediting process. We observe that, in several mouse tumour models such as HA-expressing 4T1 mammary carcinoma cells, OVA-expressing EG7 lymphoma cells and CMS5 MCA-induced fibrosarcoma cells naturally expressing mutated extracellular signal-regulated kinase (ERK) antigen, the action of antigen-specific cytotoxic T cell (CTL) in vivo results in the emergence of resistant cancer cell clones only in the presence of IFN-γ within the tumour microenvironment. Moreover, we show that exposure of tumours to IFN-γ-producing antigen-specific CTLs in vivo results in copy-number alterations (CNAs) associated with DNA damage response and modulation of DNA editing/repair gene expression. These results suggest that enhanced genetic instability might be one of the mechanisms by which CTLs and IFN-γ immunoedits tumours, altering their immune resistance as a result of genetic evolution. T cell mediated anti-tumour immune responses result in the emergence of an immune-resistant population in a process called immunoediting. Here, the authors show that immunoediting is associated with an increase in genomic rearrangements of tumour cells that requires both cytotoxic T cells and IFNγ exposure.

D -amino acids ( D -AAs) have various biological activities, such as activation of N -methyl- D -aspartic acid (NMDA) receptor as a co-agonist by D -Ser. Since several free D -AAs are released in the broth monocultured with bacterium and D -AAs are probably utilized for bacterial communication, we presume that intestinal microbiota releases several kinds of free D -AAs, which may be involved in the hosts’ health. However, presently, only four free D -AAs have been found in the ceacal lumen, but not in the colonic lumen. Here, we showed, by simultaneous analysis of chiral AAs using high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS), that 12 free D -AAs ( D -Ala, D -Arg, D -Asp, D -Gln, D -Glu, D - allo -Ile, D -Leu, D -Lys, D -Met, D -Phe, D -Ser, and D -Trp) are produced by intestinal microbiota and identified bacterial groups belonging to Firmicutes as the relevant bacterial candidates.

From a mouse triple‐negative breast cancer cell line, 4T1, we previously established 4T1.3 clone with a high capacity to metastasize to bone after its orthotopic injection into mammary fat pad of immunocompetent mice. Subsequent analysis demonstrated that the interaction between cancer cells and fibroblasts in a bone cavity was crucial for bone metastasis focus formation arising from orthotopic injection of 4T1.3 cells. Here, we demonstrated that a member of the adhesion G‐protein–coupled receptor (ADGR) family, G‐protein–coupled receptor 56 (GPR56)/adhesion G‐protein–coupled receptor G1 (ADGRG1), was expressed selectively in 4T1.3 grown in a bone cavity but not under in vitro conditions. Moreover, fibroblasts present in bone metastasis sites expressed type III collagen, a ligand for GPR56/ADGRG1. Consistently, GPR56/ADGRG1 proteins were detected in tumor cells in bone metastasis foci of human breast cancer patients. Deletion of GPR56/ADGRG1 from 4T1.3 cells reduced markedly intraosseous tumor formation upon their intraosseous injection. Conversely, intraosseous injection of GPR56/ADGRG1‐transduced 4T1, TS/A (mouse breast cancer cell line), or MDA‐MB‐231 (human breast cancer cell line) exhibited enhanced intraosseous tumor formation. Furthermore, we proved that the cleavage at the extracellular region was indispensable for GPR56/ADGRG1‐induced increase in breast cancer cell growth upon its intraosseous injection. Finally, inducible suppression of Gpr56/Adgrg1 gene expression in 4T1.3 cells attenuated bone metastasis formation with few effects on primary tumor formation in the spontaneous breast cancer bone metastasis model. Altogether, GPR56/ADGRG1 can be a novel target molecule to develop a strategy to prevent and/or treat breast cancer metastasis to bone. GPR56/ADGRG1 expression conferred growth advantage on breast cancer cells in the bone cavity, thereby promoting bone metastasis formation.GPR56/ADGRG1 can be a novel target molecule to develop a strategy to treat breast cancer metastasis to bone.